Generally, pipelines are used to transport fluids, including but not limited to oil and gas from wells. In order to measure the flow rate of these fluids in the pipeline, orifice plates are installed in a special fitting, or orifice plate carrier, and are thereafter installed in-line within the pipeline sections. When placed within the pipeline and in the fluid flow path, the orifice plates somewhat restricts the flow. Thereafter, a flow pressure differential develops between the flow on the upstream and downstream side of the orifice plate. Based on this measurement, and the comparison of the cross-sectional area of the pipeline to the cross-sectional area of the smaller through hole formed in the orifice plate, the flow rate of the fluid can be determined.
In many pipelines which must have their flow measured, it is very expensive or time consuming to shut down the pipeline to change the orifice plate, or make other required repairs thereto. Since the orifice plate must be placed within the pipeline in order to measure the flow of the fluid, it has been found to be beneficial to allow for the removal and replacement of such orifice plates without depressurizing the flow of fluid, and emptying the pipeline. Therefore, while early orifice plates have been situated within the pipes, and have required the shutdown of the pipe in order to change orifice plates, more recently, systems have been designed to allow for the insertion and removal of orifice plates in the pipeline without interrupting flow of the fluid therethrough.
In order to properly employ such a system which allows for the insertion and removal of such an orifice plate without interrupting the flow of the fluid, a number of features in the system are required. First, it is necessary to have a first chamber which encompasses the fluid flow path through the pipeline and second chamber, selectively spaced apart from the first chamber, which does not encompass the fluid flow path through the pipeline. These chambers must be selectively maintained either in fluid communication with each other or sealed from each other, and must be maintained in a fluid tight state even under high pressure as applied by the fluid flow in a pipeline. The system must allow for the movement of the orifice plate from the pipeline and first chamber, into the second chamber which can thereafter be separated from the first chamber by a fluid tight seal, and thereafter opened so that the orifice plate may be replaced, repaired or simply removed. Such systems have been well known in the art, and are shown in U.S. Pat. No. 5,318,073 (Kendrick, et al.) and any number of “senior” orifice fittings (senior referring to a dual chamber system), as are produced by Daniel, Perry Equipment Corporation and various other manufacturers.
As noted above, each of these apparatuses work with the requirement of a fluid tight seal between a first chamber, which is in fluid communication with the pipeline and encompasses the fluid flow path of the pipeline, and a second chamber which may be placed selectively in and out of fluid communication therewith. In order to achieve such a seal, prior art dual chamber orifice fittings rely on a sliding valve which requires the addition of grease or other sealing fluid thereto in order to insure that the valve slides properly and forms a fluid tight seal when closed. Such a sealing member is shown as closing valve V in U.S. Pat. No. 4,014,366 (Critendon). This patent describes a sliding valve fitting as is used in the prior art, whereby a sliding valve plug portion contains teeth on a portion thereof, which are meshed with a gear and rotating handle, or other automatic rotation device. By rotating this handle or device, the user moves the sliding valve plug portion against the passage between the first and second chambers, and thereby seals the second chamber from the first chamber. However, devices utilizing such a sliding mechanism has suffered from a number of defects.
First, the time required to move such a valve portion into position is great. Additionally, such a device utilizes a plurality of gears, racks and pinions complicating the device and requires the regular insertion of grease or other sealing fluid into the apparatus in order to preserve a fluid tight seal between the sliding valve plug mechanism and the casing forming the passage between the first and second chambers. Finally, since such a sliding valve plug device requires the determination by an operator whether the required fluid tight seal has been formed, and whether the sliding valve plug portion has been moved into its proper position, it is possible that the fluid flow could be released before the seal has been formed, thereby allowing fluid under pressure from the pipeline to escape and thereby not be contained within the pipeline or fitting causing a potentially dangerous situation. Therefore, it would be beneficial to provide a valve mechanism for sealing between a first and second chamber of a dual chamber orifice fitting which could be moved into place quickly, which does not require any insertion of grease or other lubrication substance, and which is simple in design and is automatically placed into the proper position to seal the chamber so that fluid cannot escape. Additionally, it would be beneficial to provide a safety locking mechanism so that the valve mechanism could not be moved from its sealed position accidentally.
The accuracy of the measurement given by the dual chamber orifice fitting depends on a large number of factors, including, as noted above, the ratio of the cross-sectional area of the through hole formed in the orifice plate to the cross-sectional area of the pipeline through which the fluid is flowing, and additionally the centering of the through hole formed in the orifice plate with the fluid flow path, and the leakage of any fluid around the orifice plate which does not flow through the through hole formed in the orifice plate.
Thus, to ensure that the orifice plate properly measures the fluid flowing in the pipeline, it is necessary to ensure that all of the fluid flowing through the pipeline is directed through the through hole formed in the orifice plate and that none is allowed to flow through the pipeline without passing through this through hole in the orifice plate. It is also necessary to insure that the seal holding the orifice plate remain fluid tight, thereby not allowing any fluid to flow through the pipeline other than through the through hole formed in the orifice plate. Such a seal member for an orifice plate is shown in U.S. Pat. No. 5,318,073 issued to Kendrick, et al., wherein a seal member is shown which extends on the upper and lower surface of an orifice plate, in order to ensure that the orifice plate is maintained in contact with solid portions of the pipe so as to ensure that fluid does not flow therebetween. While such a design has been somewhat satisfactory, such a design is most effective upon proper placement of the seal within the chamber in the pipe.
However, during insertion of the orifice plate while the fluid is flowing through the pipe, it is possible that the seal member could be improperly deformed due to the downward movement of the orifice plate and seal member through the laterally moving fluid in the pipeline. If improperly deformed, it is possible that the seal will not be properly seated, and therefore will allow fluid to pass between the seal and the orifice plate, and not direct all of the fluid through the through hole formed in the orifice plate, thereby affecting the accuracy of any fluid flow measurement. Therefore, it would also be beneficial to provide a seal member for an orifice plate which will not improperly deform when the orifice plate is inserted into a pipe under pressurized fluid conditions and which would therefore properly seal the orifice plate to the pipeline and increase the accuracy of measurement of fluid flow.
Finally, a further requirement of proper fluid flow measurement is that the through hole formed in the orifice plate through which the fluid is directed must remain properly centered in the pipeline and in the fluid flow path. However, since the orifice plate is being inserted into the pipeline and the fluid flow path under pressure, it is possible that the orifice plate might not be precisely centered within the fluid flow path. This off-center positioning may result in inaccurate measurement of fluid flow rates. Therefore, it would further be desirable to provide an orifice plate whose position can easily be adjusted while the orifice plate remains within the carrier plate.
In prior art dual chamber orifice fittings, the second, or upper, chamber is formed with two selectively openable valves. The first is an equalization valve. The use of this valve allows for the equalization of pressure between the first and second chamber, thereby allowing fluid into the second chamber, without removing the seal between the first and second chambers. The second, is a bleeding, or evacuation valve whereby after the orifice plate is moved from the first chamber to the second chamber, and the seal between the first chamber and the second chamber is replaced, the fluid maintained within the second chamber is evacuated in order to reduce the pressure therein. While the prior art devices utilize two valves for this purpose, it is possible, through operator error, to open both valves at the same time, thereby allowing material to flow under high pressure from the first chamber into the second chamber, and to be forced out the evacuation valve, thereby causing a potentially dangerous situation. Therefore, it would be desirable to provide a system whereby it is not possible for there to be communication between the first and second chambers, and between the second chamber and external atmosphere at the same time.
The above described deficiencies were addressed, to great extent, by U.S. Pat. No. 5,836,356 (the '356 patent), by Ashvin D. Desai, which is incorporated herein in its entirety. The '356 patent described a dual chamber orifice fitting comprising a first chamber maintained in fluid communication with a pipeline, a fluid flowing in the pipeline passing through the first chamber; a second chamber selectively maintained in fluid communication with the first chamber; a sealing member selectively rotatable from a first position wherein the sealing member seals the first chamber from the second chamber, and a second position wherein the sealing member permits the first chamber to be placed in fluid communication with the second chamber.
The components in devices such as described in the '356 patent must tolerate high pressures, temperatures, corrosive and sometimes lethal fluids, and preferably should be capable of extended use with few failures. Thus, there is a continuing need for improving the design and materials of such components with the goal of reducing the failure rate of the device as well as improving the safety of operating and servicing the device.